The invention relates to instruments for measuring and recording of environmental conditions. Specifically, this invention relates to electronic logging instruments for use in the bottom of oil wells or the like for sensing, digitizing, and compensating for any anomaly, and recording pressure and temperature conditions.
It is imperative that the parameters of an oil bearing reservoir be measured so that the oil can be efficiently extracted from the reservoir. The parameters of the oil reservoir, in particular, the pressure, must be taken as a function of time. In addition to pressure, the temperature of the oil reservoir must be measured and used to compensate for anomalies in the pressure measurement. The most commonly used measuring instrument is a helical Bourdon tube and a chart which is driven by a mechanical clock mechanism. The temperature is measured by a different instrument in the proximity of the pressure instrument but generally at a different location. A stylus attached to the Bourdon tube inscribes the pressure response on the clock driven chart. The chart constitutes a permanent analog memory of the pressure conditions. The information contained on the chart is transcribed and processed by an operator after the chart is retrieved from the recording instrument. The evaluation of the data is lengthy in time, and the accuracy of the evaluation is subject to not only the physical conditions of the recording stylus, but also to the skill of the evaluator.
During the past decade, three electronic improvements have been introduced for digitizing and digitally recording of pressure and temperature information obtained from oil bearing reservoir. Examples of these apparatuses are described in U.S. Pat. Nos. 3,977,245; 4,033,186; and 4,195,349. U.S. Pat. No. 3,977,245 introduced the use of a random access memory as a recording medium, while U.S. Pat. No. 4,033,186 described the use of magnetic core type memory. A digitization method was introduced in U.S. Pat. No. 4,195,349 which not only used a solid state memory but provided optical encoding together with linear digital compensation techniques for compensating for temperature variations. Heretofore the use of solid state or semiconductor memories was limited because the memories were volatile in nature. Even though the prior art teachings represent important improvements in the recording of environmental conditions as well as the digitization and digital compensation of the data to be recorded, significant errors sometimes arose from the transducers and the linear compensation techniques used because of the nonlinear nature of the temperature dependencies of the pressure transducers.